Method and apparatus for blow moulding of containers with a movable base part

ABSTRACT

A method for forming plastic preforms into plastic bottles includes introducing a plastic preform to be expanded into a blow mould, wherein this blow mould has at least two side parts and a bottom part which is movable in a longitudinal direction of the plastic preform in relation to these side parts; introducing a rod-shaped body through a mouth of the plastic preform into the interior of the plastic preform; applying a first pressure to the plastic preform; applying a second pressure to the plastic preform, wherein this second pressure differs from the first pressure and is higher than the first pressure; applying a third pressure to the plastic preform, wherein this third pressure differs from the second pressure and is higher than the second pressure. After applying the third pressure to the plastic preform, the bottom part is moved in the longitudinal direction of the plastic preform towards the latter.

BACKGROUND OF THE INVENTION

The present invention relates to a method and an apparatus fortransforming plastic parisons into plastic containers and in particularplastic bottles. Such methods and apparatus have been known for a longtime from the prior art. In this case heated plastic parisons areusually introduced into blow moulds and pressurised inside these blowmoulds, so that a plastic container or a plastic bottle can be shaped.In this case different pressure stages are usually applied to theplastic parisons. Thus, it is for example known that first of all apreliminary blow moulding pressure is applied which serves for the firstexpansion of the container, followed by an intermediate blow mouldingpressure and lastly a final blow moulding pressure. Furthermore, it isknown from the prior art that for expansion of the containers aso-called stretching rod is inserted into the containers in order tostretch them. In addition, methods are also known from the prior art inwhich during the expansion process a base part of the blow mould isadvanced towards the containers. Such methods are also designated asactive base methods.

The object of the present invention is to improve such methods inparticular with regard to the shaping of the plastic containers. Inparticular the shaping of the base region of such containers should beimproved.

SUMMARY OF THE INVENTION

In a method according to the invention for transforming plastic parisonsinto plastic bottles first of all a plastic parison which is to beexpanded is introduced into a blow mould, wherein this blow mould has atleast two lateral parts and a base part which is movable relative tothese lateral parts in a longitudinal direction of the plastic parison.In a further method step a rod-shaped body is introduced through a mouthof the plastic parison into the interior of the plastic parison, inparticular in order to stretch this in the longitudinal direction. In afurther method step a first pressure is applied to the plastic parison.Furthermore, a second pressure is applied to the plastic parison,wherein this second pressure deviates from the first pressure and ispreferably higher than the first pressure. In a further method step athird pressure is applied to the plastic parison, wherein this thirdpressure deviates from the second pressure and is preferably higher thanthe second pressure.

In a first embodiment according to the invention, before the thirdpressure is applied to the plastic parison and in particular at leasttemporarily while the second pressure is applied to the plastic parison,the base part is moved towards the plastic parison in the longitudinaldirection of the plastic parison.

Thus, in this embodiment it is proposed that while the intermediate blowmoulding pressure (which is designated here as the second pressure) isapplied to the plastic parison the base part is moved towards theplastic parison. In this case it is possible and preferred that theentire advancing movement takes place during this phase, that is to sayduring the application of the second pressure, that is to say theintermediate blow moulding pressure.

However, it would also be conceivable that at least a temporalproportion of this movement also takes place in another phase forinstance while the first pressure is applied to the plastic parisonand/or while the third pressure is applied to the plastic parison.

In a second embodiment according to the invention, during and/or afterand in particular after the application of the third pressure to theplastic parison the base part is moved towards the plastic parison inthe longitudinal direction of the plastic parison.

In this embodiment the advancing of the base part takes place inparticular during a rinsing phase of the plastic container, andpreferably during a time period in which the pressure in the containerdrops again. Preferably in this case the base part can remain advancedtowards the plastic parison until the end of this rinsing phase. Duringthe rinsing phase a lower pressure prevails in the container than duringthe application of the third pressure or during the final blow moulding.Due to this lower pressure it is more easily possible to advance thebase part, since it only has to approach against a lower pressure.

In a third embodiment according to the invention, during the applicationof at least one of the pressures to the plastic parison the base part isadvanced towards the plastic parison in the longitudinal direction ofthe plastic parison in at least two time intervals spaced apart from oneanother in time.

All of the three variants according to the invention which are describedhere are distinguished in that the base part is advanced towards theplastic parison during the application of compressed air to the plasticparison. However, the respective time intervals or frequencies in whichthis advancing of the base part takes place are different. The directlyfollowing description relates to all of the aforementioned embodimentswhich are in each case applicable to all embodiments according to theinvention. Then preferred variants are described which relate to theindividual embodiments. In this case advantageously the describedpressures are not constant during the respective intervals. The firstpressure and the second pressure preferably increase in the course ofthe respective time intervals. On average, however, the second pressureis higher than the first pressure. The third pressure is advantageouslysubstantially constant over a predetermined time period.

Preferably the application of the second pressure to the plastic parisondirectly follows the application of the first pressure to the plasticparison. Preferably the application of the third pressure to the plasticparison directly follows the application of the second pressure to theplastic parison.

The changing over to the different pressures preferably takes place byoperation of valves. Thus for example in order to achieve the transitionfrom the first pressure to the second pressure a first valve, whichregulates or effects the delivery of the first pressure to the plasticparisons, can be closed and instead of this a second valve, whichregulates or effects the delivery of the second pressure, can be opened.Accordingly, during the changeover from the second pressure to the thirdpressure a valve which effects the delivery of the second pressure (moreprecisely the delivery of air under the second pressure) can be closedand instead a further valve which effects the delivery of air under thethird pressure can be opened.

Thus a transition between the individual pressures is preferablytriggered by the switching of at least one valve and preferably severalvalves.

A rinsing phase during which the plastic containers are rinsedpreferably follows the phase in which the third pressure acts on theplastic container. Also in this case this rinsing phase can be initiatedby an operation of valves, in particular in that a valve which providesthe third pressure P2 is closed and instead a valve which makes therinsing operation possible is opened. The pressure during the rinsingphase is preferably lower than the third pressure.

Thus, in the context of the method according to the invention a movementof the base part is proposed and so a movement of the base part duringthe expansion of the plastic parison is proposed. It is pointed out thatalthough the above-mentioned method steps are carried out in a specificsequence, they can also proceed simultaneously and preferably alsoproceed simultaneously. This it is for example possible that therod-like body is introduced into the plastic parison through the mouththereof and simultaneously the first pressure is applied to the plasticparison. Furthermore, it is also possible that the aforementionedpressures are not constant, but are changed, for example raised orlowered, over a certain time period.

In a further preferred method a movement of the rod-like body linearlyand/or at a constant speed takes place. This means that the rod-likebody is introduced into the plastic container with a linear movement.The rod-like body is preferably introduced so far into the plasticparison that it touches the bottom. Thus the rod-like body is suitableand intended to stretch the plastic parison in the longitudinaldirection thereof.

In a further preferred method a movement of the rod-like body takesplace linearly and/or at a constant speed. Advantageously in this casethe base part is advanced towards the plastic parison and/or in thedirection of the above-mentioned rod-like body.

In a further preferred method the shaped plastic container is removedfrom the blow mould in particular after the application of the thirdpressure (and preferably after a rinsing phase and a pressure reliefphase). The blow mould is preferably opened in order to be able tointroduce the plastic parison into it. In this case particularlypreferably a lateral part of the blow mould is pivoted relative to thesecond lateral part of the blow mould, preferably relative to an axiswhich extends parallel to a longitudinal direction of the plasticparison to be expanded. After the introduction of the plastic parisonthe blow mould is closed again in the same way by pivoting.

In a further advantageous embodiment the plastic container is movedduring its expansion on a predetermined transport path and in particularon a circular transport path.

Furthermore, it is possible that compressed air is applied to theplastic container through the rod-like body. However, it would also bepossible that the compressed air necessary for expanding the plasticparison is guided between the rod-like body and a mouth of the plasticparison. In a further preferred method the blow mould is locked beforethe air is applied, and particularly preferably the blow mould isunlocked again after the application of air and before the opening.

In a further preferred method the rod-like body is at least partiallyretracted before or during the advancement of the base part. In this waya collision between the rod-like body and the base part (optionally withthe wall of the plastic parison lying between them) is prevented.

In a further preferred method the base part is advanced by a distancewhich is greater than 5 mm, preferably greater than 10 mm andparticularly preferably greater than 15 mm and/or the base part isadvanced by a distance which is less than 30 mm, preferred less than 25mm and particularly preferably less than 20 mm. These respectiveadvancing distances also depend upon a container to be produced.However, it has been shown that these relatively small advancingdistances are particularly suitable for producing or shaping bases.

In a further preferred method the plastic parison or the containerproduced therefrom is relieved of pressure again after the applicationof the third pressure. In this way, after the final blow moulding of thecontainer, pressure can again be released from the container so thatthis can finally be removed from the blow mould. In this connection itis pointed out that in the context of the present application, for thesake of simplicity, reference is made predominantly to the applicationof pressure to the plastic parison, although starting from a certaintime (in any case already starting from the application of the thirdpressure) a shaped container is already present inside the blow mould.

In particular in the first embodiment according to the invention, thebase part is advanced at least temporarily while the second pressure isapplied to the plastic parison. In this case it is possible that thefeeding movement also takes place, still temporarily, during theapplication of the first pressure and particularly preferably theadvancing of the base part takes place during a changeover from thefirst pressure to the second pressure.

Advantageously the transitions between the individual pressures differby a slight lowering of the pressure in the course of time. Thuspreferably the respective subsequent pressure, that is to say forexample the second pressure or the third pressure, is defined startingfrom a time at which it rises again starting from a minimum value.

However, at a time at which the third pressure is reached, the base partis advantageously already completely advanced towards the plasticparison and/or moved in an upper position.

In a further embodiment the base part is advanced during a period oftime which is between one second and 20 seconds, preferably between onesecond and 15 seconds, preferably between two seconds and ten secondsand particularly preferably between two seconds and five seconds. Aspeed at which the base part is advanced towards the plastic parison isadvantageously adjustable.

In all of the above-mentioned embodiments the second pressure ispreferably greater than 3.5 bar, preferably greater than 5 bar,preferably greater than 7 bar and particularly preferably greater than10 bar and particularly preferably greater than 12 bar. Furthermore, thesecond pressure is preferably less than 20 bar, preferably less than 18bar and particularly preferably less than 17 bar.

In a further advantageous embodiment which is applicable in particularfor the second configuration described above, the rod-like body is atleast partially retracted before the application of the third pressureto the plastic parison. Advantageously, the rod-like body is retractedat least so far as is necessary in order to advance the base.Advantageously, the rod-like body is retracted completely in a furthermethod step. In this embodiment also the base part is in any caseadvanced completely in its upper position or upwards when the thirdpressure is reached. In this embodiment, during the application of thethird pressure to the plastic parison, the base part is advantageouslyadvanced completely, that is to say to the plastic parison or to thecontainer already shaped at this time.

For all the embodiments of the invention the first pressure isadvantageously in a range between 1 and 12 bar, preferably between 1 and10 bar and particularly preferably between 1 and 8 bar.

The third pressure preferably lies in a range between 15 and 50 bar,preferably between 17 and 40 bar, particularly preferably between 20 and40 bar and particularly preferably between 20 and 38 bar.

In a further advantageous embodiment which relates in particular to theabove-mentioned third embodiment of the invention, the base part is atleast partially retracted again (in the direction of a lower restposition) between the two intervals which are spaced apart from oneanother in time (in which it is advanced towards the plastic parison).Thus, in this embodiment the base part is first of all advanced towardsthe plastic parison, then at least partially retracted again, in orderto be advanced again to the plastic parison. Thus, in this embodimentthe base part is advanced towards the plastic parison a number of times.

In the third embodiment a time interval advantageously lies at leastpartially after the application of the second pressure. At least onetime interval preferably lies after the beginning of the application ofthe second pressure to the plastic parison. Thus, for example it ispossible that a first advancing movement towards the plastic parisonbegins during a preliminary blow moulding process and a furtheradvancing movement only begins at a time after the application of thesecond pressure or in a time period in which the pressure in theinterior of the plastic parison drops again.

Furthermore, it would also be possible that both advancing movementstake place at a time after the application of the second pressure to theplastic parison, and particularly preferably also at a time after thethird pressure is applied to the plastic parison. In this embodimentboth advancing movements can advantageously be carried out in a (time)interval in which a pressure inside the plastic container drops again.

In a further advantageous variant of the third embodiment, both timeintervals lie at least partially after the application of the thirdpressure. In a further embodiment, during time intervals of differentlengths, the base part particularly preferably remains in a stateadvanced towards the plastic parison. In this case it is possible thatthis first time period (in which the base part is advanced closer to theplastic parison) is longer, for example while the entire application ofthe third pressure takes place. Furthermore, it is also possible thatthe second time period is longer. It is also possible that the firsttime period is advanced only for a very short time, for example the basepart is moved upwards and is immediately moved back again.

In a further advantageous method the plastic container is applied with arinsing pressure after the application with the third pressure. Duringthis phase the pressure inside the container drops significantly. Thus,this rinsing pressure is preferably comparable with the pressure of theintermediate blow moulding, that is to say the above-mentioned secondpressure. How far the pressure in the container drops during theflushing depends upon whether or not blowing air is to be recycled. Ifsuch compressed air recycling is provided, the pressure inside thecontainer drops to approximately 15-20 bar. This correspondsapproximately to the level of the second pressure, that is to say theintermediate blow moulding pressure.

If no recycling is provided or if venting to the environment is to takeplace, the rinsing pressure drops to approximately 6-10 bar and thus isof the order of magnitude of the pressure during preliminary blowmoulding, that is to say the first pressure P1. Advantageously, thecontainer is cooled during the rinsing operation and in particular iscooled by compressed air escaping therefrom. This rinsing phase followsa pressure relief phase, during which the remaining pressure escapesfrom the container.

These individual pressures or the air are preferably provided by atleast one reservoir and preferably several reservoirs. These reservoirsmay be for example so-called annular channels which serve for storage ofair. During the application to the plastic parisons, the highestpressure preferably prevails in the reservoir or the annular channelwhich provides the second pressure. This corresponds approximately tothe third pressure, but can even be somewhat higher.

Furthermore, the present invention relates to an apparatus fortransforming plastic parisons into plastic containers with at least onetransport device on which a plurality of transforming stations arearranged, wherein each of these transforming stations has a blow mouldwhich in each case has two lateral parts, which are movable with respectto one another for opening and closing the blow mould, as well as a basepart, wherein this base part is movable relative to the lateral parts ina longitudinal direction of the plastic parison and in a closed state ofthe blow mould, and wherein the apparatus has at least one applicationdevice in order to apply a gaseous medium and in particular compressedair to the plastic parisons for expansion thereof, as well as a controldevice which controls the application of the gaseous medium to theplastic parisons in such a way that first of all a first pressure, thena second pressure which is above the first pressure, and finally a thirdpressure preferably above the second pressure, are applied to theplastic parisons.

According to the invention the apparatus has a driving device which issuitable and intended to move the base part towards the plastic parisonsat least temporarily during the application of the plastic parisons,wherein in a first embodiment according to the invention, before thethird pressure is applied to the plastic parison and particularlypreferably at least temporarily while the second pressure is applied tothe plastic parison, the base part can be advanced towards the plasticparison in the longitudinal direction of the plastic parison. In asecond embodiment according to the invention, during or after and inparticular after the application of the third pressure to the plasticparison the base part is moved towards the plastic parison in thelongitudinal direction of the plastic parison.

In a third embodiment according to the invention, the base part can beadvanced towards the plastic parison in the longitudinal direction ofthe plastic parison in at least two time intervals spaced apart from oneanother in time.

In this case the second advance preferably serves to produce a kink inthe base region.

Advantageously, the apparatus has a rod-like body which, during theexpansion of the plastic parisons, can be introduced into the plasticparisons in order to stretch them. The apparatus advantageously also hasa driving device for driving this rod-like body. This driving device canbe in particular, but not exclusively, an electric motor-powered,hydraulic, pneumatic or magnetic driving device. The apparatusadvantageously has a control device which also controls the movement ofthis rod-like body. Advantageously, a movement of the rod-like body isat least temporarily adapted to a movement of the base part. This meansthat the rod-like body for example can be retracted by the same range bywhich the base part is advanced.

In a further advantageous embodiment the two lateral parts are pivotablewith respect to one another and particularly preferably are pivotablewith respect to an axis which is parallel to a longitudinal direction ofthe plastic parison.

Therefore within the context of the invention, a process cycle isdescribed in relation to a so-called active base/overstroke method. Inthis case the base lift is limited to a range between 14.9 mm and 19.9mm. In a method according to the invention, first of all the plasticparison is placed in the blow mould and preferably then the blow mouldis closed and locked. In this phase of the method the base part or thebase mould is in its lower end position.

Then the rod-like body or the stretching rod is inserted so far into theplastic that it touches a ridge of the plastic parison. Subsequently theapplication of the first pressure, that is to say the preliminary blowmoulding, is started. In this case it is also possible that thisapplication is already started with the pressure before the rod-likebody is inserted. In this way at a low pressure the blowing or the blowmoulding process can be monitored.

In a further method step, in the embodiment according to the invention,in particular before the initiation of a lifting of the base and/or anapplication of the second pressure, the rod-like body or the rinsing rodis raised and in particular moved into a position of base located in orcoming to the end position.

Then the base part is preferably advanced towards the plastic parison ormoved into its upper end position. In a further method step a final blowmoulding with the third pressure takes place. This movement of the basepart into its highest position preferably takes place during theintermediate blow moulding with the second pressure. Beyond the end ofthe third pressure phase (the final blow moulding) the base part ispreferably located in its highest position. In a further method step arinsing takes place, wherein here the rinsing rod or the rod-like bodyis particularly preferably in a retracted position. Finally the rod-likebody also moves back again.

In particular in the second embodiment, after the preliminary blowmoulding and the stretching, an intermediate blow moulding takes place,that is to say an application of the second pressure P2 to the plasticparison. Advantageously in this phase of the method the rod-like bodymoves back at least partially.

In this embodiment, after the application of the third pressure and inparticular during rinsing the base is moved into an upper position.However, this can also be initiated already just before the start of therinsing.

With this embodiment a standard process preferably runs until the end ofthe application of the third pressure, or a process which only differsin the stretching path, that is to say the movement path of the rod-likebody differs from a standard process. Advantageously, during anintermediate blow moulding, that is to say during the application of thesecond pressure the rod-like body is moved back, for example to aposition explained more precisely below. After the application of thethird pressure to the plastic container, a rinsing phase preferablytakes place in which the pressure is again lowered and in particular arinsing of the container occurs. During this phase the base part israised into a so-called boxing phase.

Advantageously, an internal pressure of the container or a rinsingpressure in this phase is between 4 bars and 20 bar, preferably between6 and 12 bar.

In a further preferred method the base part is moved upwards again afterthe end of flushing.

This embodiment also offers the advantage that less force is necessaryfor advancing the base part. Also in this way less pressure is requiredin an overstroke unit. Finally, wear of the entire system (seals andstops) can also be reduced. In addition, a better control can also beachieved, since the contour is completely blown out. Finally, tensionscan also be reduced, since the material can relax for longer.

In a further preferred method, which relates in particular to the thirdembodiment according to the invention, the base part is moved during theintermediate blow moulding, that is to say during the application of thesecond pressure, to a high end position and thus stretches the base ofthe container. Then a rinsing operation takes place and the base part isagain moved into its highest and then into its lowest end position, inorder to create a fold point, at which the base can be hinged inwardsmore easily. The end of the blow moulding process takes place in turn asis known from the prior art.

In a second variant a standard process as described above is carried outup to and including the end of the final blow moulding. This means thatthe base remains in its lowest end position until the end of theapplication of the third pressure. As mentioned above, this end positioncan again be located between 14.9 mm and 19.9 mm below the stretchingrod position. Then during the rinsing operation the base part is movedinto its highest end position and thus the bottom of the container isstretched. After the final stretching the base part moves back into itslowest end position. Now an operation for generation of the kink takesplace. For this purpose the base part is moved again into its highestend position and then again into its lowest end position, in order thusto create the kink. This generation of the kink can also take place bymultiple repetitions of the movement of the base mould. Then the basepart and the stretching rod are moved into their process terminationposition and the finished container is discharged and transferred tofurther handling systems.

After this method step, in all embodiments a pressure relief cycle isrun through and after the end of this pressure relief cycle the basepart is again moved into its lower position. Lastly, after the openingof the blow mould the plastic container is removed as a finally blowmoulded bottle. An improved control of the blow moulding speed isachieved by the present invention. A further control can preferably takeplace by an adjustment of the second pressure P2. In addition, a largerprocess window is made possible, since the blowing can develop moreslowly. In this way a higher container quality is also achieved. Animproved control of the wall thicknesses can also take place, inparticular more constant wall thicknesses can be achieved. This secondpressure P2 is partially also designated as intermediate blow mouldingpressure (Pi).

Further advantages exist in that a lower force is necessary during theso-called boxing, that is to say during the movement of the base part,since at the highest third pressure it is not necessary to move againstit. In this way the entire transforming station can also be designed forpressures below 30 bar. Less pressure is required and also theassemblies are less stressed.

Preferably it is possible that the base part or a base lifting unit ismoved with different pressures, so that the speed of the lifting can beinfluenced. Furthermore, it is also possible that with the secondpressure the speed of the blowing or of the blow moulding process isinfluenced. In this way larger process windows can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and embodiments are apparent from the appendeddrawings.

In the drawings:

FIG. 1 shows a roughly schematic representation of a system forproducing plastic containers;

FIG. 2 shows a schematic representation of a transforming station;

FIG. 3 shows two representations for illustrating the production of thecontainers;

FIG. 4 shows a representation of a method in a first embodimentaccording to the invention;

FIG. 5 shows a representation of a method according to the invention ina second embodiment;

FIG. 6 shows a representation of a method according to the invention ina third embodiment according to the invention;

FIG. 7 shows a representation of a method according to the invention inthe third embodiment; and

FIG. 8 shows a further representation of a method according to theinvention in the third embodiment.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows quite schematically an apparatus 1 according to theinvention for producing plastic containers. This apparatus has a carrier2 which is rotatable with respect to an axis of rotation Z and isconfigured here as a so-called blow moulding wheel. A plurality oftransforming stations 20 are arranged on this blow moulding wheel.During the transformation of the plastic parisons to plastic containersthese transforming stations are moved along the transport path P, thatis to say along a circular path.

FIG. 2 shows a schematic representation of a transforming station 20 ora half of such a transforming station. This has two lateral part carrierparts of which, however, only one lateral part carrier part 4 is shown.These lateral part carrier parts serve in each case for holding blowmould lateral parts, wherein here too only the blow mould lateral part14 is represented. These blow mould lateral parts form, together with abase part 18, a cavity 15 within which the plastic parisons 10 can beblow moulded to form plastic containers. The reference L relates to alongitudinal direction of the plastic parison. Between the lateral partcarrier part 4 and the blow mould lateral part 14 there is arranged ablow mould support shell 16 (and correspondingly also between the secondlateral part carrier part (not shown) and the second blow mould lateralpart (not shown)).

The reference numeral 32 designates a blow moulding nozzle which servesfor application of compressed air to the plastic parisons. By means ofthis application device the individual air pressures can be applied tothe plastic parison. The reference 34 designates the rod-like body orthe stretching rod which can be introduced into the container. The basepart 18 can be moved by a driving device 36, only schematicallyillustrated, in the longitudinal direction L relative to the lateralparts. A movement towards the plastic parison is understood in FIG. 1 tobe a movement upwards.

FIG. 3 shows two representation of a plastic container. In this case theleft-hand representation shows a geometry of the container before theboxing phase during rinsing.

The right-hand representation shows a situation after the boxing phase,in which the base 10 a of the container was pushed upwards in order togenerate a kink.

FIG. 4 shows a first representation of a method according to theinvention. In this case the reference 52 relates to the blow mouldingcurve or the pressure profile.

The references P1, Pi, P2, Sp and E or the corresponding vertical linesdesignate respective time periods, from which in each case new pressurestages are used. The second pressure Pi is also designated asintermediate blow moulding pressure. It will be recognised that startingfrom a time of approximately three seconds a specific pressure P1, thepreliminary blow moulding pressure, is applied to the plastic container.At the same time the stretching rod is moved into the container. Thereference 54 designates the course of the stretching rod movement.Towards the end of the phase in which the first pressure P1 is applied,the rod-like body is retracted slightly and offset for a short time andalso the base part is moved into an upper position.

The entire pressure profile preferably has several inflection points (inthe mathematical sense, i.e. points at which the second derivative of acorresponding function would change the plus/minus sign). Preferably, bydefinition, the first pressure P1 transitions into the second pressurePi in the region of an inflection point WP1 of the pressure, and in turnthis second pressure Pi transitions into the third pressure P2 in thecourse of an inflection point WP2. The transition from the thirdpressure P2, which is also designated as the final blow mouldingpressure, to the rinsing pressure Sp takes place just before a markeddrop in the pressure, and in turn the transition from the rinsingpressure Sp to the relief pressure takes place before a marked drop inthe pressure.

Accordingly, the reference 56 designates the course of movement of thebase part. Furthermore, it will be seen that in this embodiment duringthe complete phase of the application of the third pressure P2 to thecontainer the base part remains in the upwardly advanced position. Thethird pressure P2 first of all rises to a specific level ofapproximately 35 bar and remains in this phase for a predetermined timeperiod, in this case approximately 12 seconds. In this time interval thecontainer is shaped extensively. After this final blow moulding arinsing of the container (pressure Sp) takes place, wherein here thepressure again drops to a level of approximately 10 bar. Lastly, in afinal phase E (or during an application of the relief pressure E) thecontainer is relieved and the stretching rod is retracted again upwards.In this phase the base part is also retracted again, as can be seen fromthe last portion of the curve 56.

FIG. 5 shows a further embodiment of the method according to theinvention. The pressure profile 52 is as already described in thepreceding method, that is to say that there are no changes here. Also,as in the embodiment shown in FIG. 4, the stretching rod is stillretracted a little during the application of the first pressure P1 tothe container. The reference P10 designates the position to which thestretching rod is retracted. The reference P0 designates a furtherposition of the stretching rod.

Unlike the embodiment shown in FIG. 4, in the embodiment shown in FIG. 5the base part here is only advanced upwards during the rinsing phase orthe pressure Sp and is reset again during the pressure relief phase E.Thus, in this method, for the entire duration of the application ofpressure to the plastic parison or the plastic bottle the base partremains in an (upper) state in which it is advanced towards the plasticbottle.

With regard to the pressure profiles, in all embodiments it can be seenthat, as mentioned 20 above, these pressure profiles in each case adjoinone another. In any case, however, an average pressure in the individualphases (preliminary blow moulding, intermediate blow moulding and finalblow moulding) is different, that is to say the preliminary blowmoulding pressure in this case is lower than the intermediate blowmoulding pressure on average and the intermediate blow moulding pressureis on average lower than the final blow moulding pressure. In otherwords, the average pressure between the vertical lines P1 and Pi wouldbe lower than the average pressure between the vertical lines Pi and P2and this in turn would be lower than the average pressure between thevertical lines P2 and Sp. The average pressure between the lines Sp andE in turn is lower than the average pressure between the lines P2 andSp.

In the method shown in FIG. 6 the base part is first of all advancedtowards the plastic parison before or during the application of thesecond pressure, and remains in this upwardly placed position until theapplication of the third pressure P2 is complete. Then, in the regionbetween the vertical lines Sp and E the base part is briefly reset toits starting position and then advanced again towards the plasticparison. This takes place in the region of the pressure relief phase E.Lastly the base part is still pushed back into its starting positionduring the pressure relief phase. The stretching rod movement preferablydoes not follow these last described movements of the base part, butremains in a partially retracted position. Thus in this method the basepart is advanced towards the plastic parison and also retracted againprecisely twice. However, it would also be possible that the base partis advanced towards the plastic parison and (at least partially)retracted again more frequently than twice, for example three times orfour times.

FIG. 7 shows a further embodiment in a variant of that shown in FIG. 6.Also in this embodiment the base part is advanced and retracted againtwice, albeit only after the application of the third pressure P2. Itwill be seen that here the base part is briefly advanced towards theplastic parison and immediately retracted again, in order then to beadvanced once again towards the plastic parison or the now shapedplastic container. Also in this embodiment the base part is finallymoved back again into its starting position.

FIG. 8 shows a further embodiment of the method shown in FIG. 6. It willbe seen that here the base part is first of all advanced during the P1phase and the beginning Pi phase. Then, during the application of thethird pressure P2 to the plastic parison, the base part is brieflyretracted and again advanced towards the plastic parison. For a thirdtime the base part is retracted during the rinsing phase Sp in orderthen to be advanced again towards the plastic parison (or towards thecontainer which is already shaped at this time) during the pressurerelief phase. Thus, in the method shown in FIG. 8 the base part isadvanced towards the plastic parison and retracted again precisely threetimes. In this method a better control of the blow moulding speed isalso possible. In particular control by adjustment of the secondpressure Pi (that is to say the intermediate blow moulding pressure) ispossible. Also in this way the container quality can be improved. Abetter control of the wall thicknesses is also possible.

The applicant reserves the right to claim all the features disclosed inthe application documents as essential to the invention in so far asthey are individually or in combination novel over the prior art.Furthermore it is pointed out that features which may be advantageousper se have also been described in the individual drawings. The personskilled in the art recognises immediately that a specific featuredescribed in a drawing may also be advantageous without theincorporation of further features from this drawing. Furthermore theperson skilled in the art recognises that advantages may also resultfrom a combination of several features shown in individual drawings orin different drawings.

LIST OF REFERENCES

-   1 apparatus-   2 carrier-   4 lateral part carrier-   10 plastic bottle (also plastic parison)-   10 a container base-   14 blow mould lateral part-   16 support shell-   18 base part-   15 cavity-   20 transforming stations-   32 blow moulding nozzle-   34 rod-like body, stretching rod-   36 driving device for movement of the base part 18-   52 curve of the pressure profile-   54 course of the stretching rod movement-   56 course of the movement of the base part-   P1 first pressure, preliminary blow moulding pressure-   Pi second pressure, intermediate blow moulding pressure-   P2 third pressure, final blow moulding pressure-   Sp rinsing pressure-   E relief (pressure)-   P0, P10 positions of the stretching rod-   Z axis of rotation-   P transport path-   WP1,WP2 inflection points of the pressure profile curve

The invention claimed is:
 1. A method for transforming plastic parisonsinto plastic bottles, comprising the following steps in sequence:introducing a plastic parison which is to be expanded into a blow mould,wherein the blow mould has at least two lateral parts and a base partwhich is movable relative to the lateral parts in a longitudinaldirection (L) of the plastic parison, inserting a rod-shaped body intoan interior of the plastic parison through a mouth of the plasticparison, applying a first pressure (P1) to the plastic parison, applyinga second pressure (Pi) to the plastic parison, wherein this secondpressure (Pi) deviates from the first pressure (P1) and is higher thanthe first pressure (P1), applying a third pressure (P2) to the plasticparison, wherein this third pressure (P2) deviates from the secondpressure (Pi) and is higher than the second pressure (Pi), wherein onlyafter the third pressure (P2) is applied to the plastic parison, thebase part is advanced towards the plastic parison in the longitudinaldirection (L) of the plastic parison.
 2. The method according to claim1, wherein the rod-shaped body is at least partially retracted before orduring the advancement of the base part.
 3. The method according toclaim 1, wherein the base part is advanced by a distance which isgreater than 5 mm, preferably greater than 10 mm and particularlypreferably greater than 15 mm and/or that the base part is advanced by adistance which is less than 30 mm, preferably less than 25 mm andparticularly preferably less than 20 mm.
 4. The method according toclaim 1, wherein after the application of the third pressure (P2) theplastic parison is again relieved of pressure.
 5. The method accordingto claim 1, wherein the base part is retracted again after theapplication of the third pressure (P2) to the plastic parison.
 6. Themethod according to claim 1, wherein before the application of the thirdpressure (P2) to the plastic parison, the rod-shaped body is at leastpartially retracted.
 7. The method according to claim 1, wherein thebase part is advanced for a duration which is between 1 sec and 20 sec,preferably between 1 sec and 15 sec and preferably between 2 sec and 10sec and particularly preferably between 2 sec and 5 sec.
 8. The methodaccording to claim 1, wherein the second pressure is greater than 3.5bar, preferably greater than 5 bar, preferably greater than 7 bar andparticularly preferably greater than 10 bar and preferably greater than12 bar and/or the second pressure is less than 20 bar, preferably lessthan 18 bar, and particularly preferably less than 17 bar.
 9. The methodaccording to claim 1, wherein after the application of the thirdpressure (P2) a rinsing pressure (Sp) is applied to the plastic parison.10. The method according to claim 5, wherein the base part is retractedagain after rinsing of the plastic parison.
 11. The method according toclaim 5, wherein the base part is retracted again during pressure reliefof the plastic container produced from the plastic parison.
 12. Themethod according to claim 1, wherein after the third pressure (P2) isapplied to the plastic parison, the base part is at least twice advancedtowards and at least twice partially retracted from the plastic parisonwith the longitudinal direction of the plastic parison.
 13. An apparatusfor transforming plastic parisons into plastic bottles, the apparatuscomprising: at least one transport device on which a plurality oftransforming stations are arranged, wherein each of the transformingstations has a blow mould, each of which has two lateral parts, whichare movable with respect to one another for opening and closing the blowmould; a base part, wherein the base part is movable relative to thelateral parts in a longitudinal direction (L) of the plastic parison andin a closed state of the blow mould; at least one application deviceconfigured to apply a gaseous medium to the plastic parisons forexpansion thereof; a control device which controls the application ofthe gaseous medium to the plastic parisons, wherein, first of all, afirst pressure (P1), then a second pressure (Pi) which is above thefirst pressure (P1), and finally a third pressure (P2) preferably abovethe second pressure (Pi), are applied to the plastic parisons; and adriving device configured to move the base part at least temporarilyduring the application of pressure to the plastic parisons, wherein onlyafter the third pressure (P2) is applied to the plastic parison, thebase part is advanced towards the plastic parison in the longitudinaldirection (L) of the plastic parison.
 14. The apparatus of claim 13,wherein the driving device is configured to move the base part at leasttemporarily during the application of pressure to the plastic parisons,wherein after the third pressure (P2) is applied to the plastic parison,the base part is at least twice advanced towards and at least twicepartially retracted from the plastic parison in the longitudinaldirection (L) of the plastic parison.